Pediatric intensive care admissions for severe acute asthma during the COVID-19 pandemicSomayeh Bazdar1, 2, 3*, Sarah van den Berg4, 5*, Niels W. Rutjes4, Lizan D. Bloemsma1, 2, 3, George S. Downward6, 7, Letty A. De Weger8, Suzanne W.J. Terheggen-Lagro3, Yolanda de Wit-van Wijck1, 2, 3, Anke H. Maitland van der Zee1, 2, 3,4, Berber Kapitein5Department of Pulmonary Medicine, Amsterdam UMC, Amsterdam, The NetherlandsAmsterdam Institute for Infection and Immunity, Amsterdam, The NetherlandsAmsterdam Public Health, Amsterdam, The NetherlandsDepartment of Pediatric Pulmonology, Emma Children’s Hospital, Amsterdam UMC, University of Amsterdam, Amsterdam, The NetherlandsPediatric Intensive Care Unit, Emma Children’s Hospital, Amsterdam UMC, University of Amsterdam, Amsterdam, The NetherlandsDepartment of Environmental Epidemiology, Institute for Risk Assessment Sciences (IRAS), Utrecht University, Utrecht, The NetherlandsJulius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht, The NetherlandsLeiden University Medical Center, Department of Pulmonology and Department of Public Health and Primary Care, Postbus 9600, 2300 RC Leiden, The Netherlands* Co-first author: Both Somayeh Bazdar and Sarah van den Berg are first authors and contributed equally.Running title : Severe acute asthma during COVID-19

Background – The incidence of pediatric asthma exacerbations during the COVID-19 pandemic has been evaluated; however, the incidence of severe acute asthma (SAA) requiring a Pediatric Intensive Care Unit (PICU) admission is unknown. Furthermore, we examined several factors which might influence this incidence, such as environmental triggers or changes in COVID-19 lockdown regulations. Methods – In this single-center, retrospective cohort study running from 2018 to 2021, all PICU admissions for SAA of children above two years of age at a tertiary hospital in the Netherlands were included. Information on potential asthma triggers during the pandemic, including viral infections, concentrations of ambient fine particulate matter (PM2.5) and pollen index were evaluated. Results – In total, 168 children were included in this study. While we observed a decrease in PICU admissions for SAA during lockdown periods, there was an increase in the admission rates in the periods without a lockdown, with the highest peak from August to November of 2021. This peak in the fall of 2021 did not align with pollen or ambient PM2.5 concentrations (r s=-0.04 for pollen and r s=0.23 for PM2.5). Discussion – COVID-19 lockdowns influenced the admission rates for SAA at the PICU both during and after the lockdowns in the Netherlands. We hypothesize that an increase in viral infections after lockdown periods was the reason for the altered incidence of SAA at the PICU in late 2021, rather than air pollution and pollen concentrations.